Chromium electroplating



3,041,257 Patented June 26, 1962 This invention relates to theelectrodeposition of chromium from aqueous acidic hexavalent chromiumbaths and has particular reference to aqueous acidic hexavalent chromiumbaths comprising a stable additive composition for the bath which iscapable of reducing substantially the formation of spray and mist duringelectrolysis.

It is well known in the art that large quantities of hydrogen areevolved at the cathodes and largequantities of oxygen and ozone areevolved at the insoluble anodes during the electrodeposition of chromiumfrom aqueous acidic hexavalent chromium solutions or baths. Anundesirable spray and mist of chromic acid is given off from the bath asthe-many gasfbubbles formed by the relatively large quantities ofhydrogen, oxygen and ozone burst violently at the. surface of the bath.

, The spray and mist that is given oil? during electrolysis is ofconsiderable volume, and is highly toxic to the workers in and aroundthe area of the spray. Furthermore, the mist is highly corrosive tonearby equipment, and has a deleterious contaminating effect on otherplating baths in the vicinity.

Many attempts have been made by those skilled in the art to prevent orto minimize substantially the formation of this highly undesirablesprayand mist during the electrodeposition of chromium from aqueousacidic hexavalent chromium solutions. The methods proposed heretoforehave not been entirely satisfactory.

This invention is concerned particularly with providing a stableadditive composition for acidic hexavalent chromium baths which iscapable of minimizing substan tially the formation of spray and mistduring electrolysis of such baths with insoluble or highly polarizedanodes, and to provide a new and improved hexavalent chromium v platingbath.

For a complete understanding of this invention, reference is made to thefollowing detailed description.

In accordance with this invention stable additive compositions foraqueous acidic hexavalent chromium electroplating baths have been foundthat are highly satisfactory in preventing substantially the formationof spray and mist during electrolysis.

Chromium elect'ropolating baths are well known in the art, and basicallythey comprise chromium trioxide, C chrornic acid or chromic anhydride,Water, and a catalyst. There would be no chromium deposited from thebath without the catalyst. The addition of a suitable catalyst in theratio of about 1 part by Weight to 100 parts by weight of chromic acidproduces a satisfactory working solution. The above ratio can be variedto meet different plating conditions. Thus, the ratio has been varied bythose skilled in the art from about 1:60 to 1:250. V

The catalyst'employed in the chromium electroplating bath can be asulfate, usually introduced into the bath by the addition of sulfuricacid.

Sorhe common formulations are as follows: (i) 33 ounces of chromic acidper gallon of electrolyte and 0.33

ounce of sulfuric acid (98%) per gallon of electrolyte; (ii) 54 ouncesof chromic acid per gallon of electrolyte and 0.54 ounce of sulfuricacid (98%) per gallon of electrolyte; and (iii) 40 ounces of chromicacid per gallon of electrolyte and 0.40 ounce of sulfuric acid (98%)gallon of electrolyte.

formation of spray Chromium electroplating baths can be prepared bysupplying CrO in the form of chromic anhydride or in the form ofcompounds containing cations which do not affect adversely the bathcharacteristics. Such compounds include the chromates, dichromates, andpolychromates of potassium, sodium, magnesium and calcium. The CrO canbe added in the form of chromic acid and/or dichromic acid in solution.Where alkali metal cations are present, the bath should not beneutralized in excess of of the dichromate end-point.

Sulfate ions can be added in the form of sulfuric acid as above setforth or as a sulfate salt or salts with a cation that does not affectadversely the characteristics of the bath. Examples of such cationsinclude potassium, sodium, calcium, strontium, magnesium, and chromium.

Silicofiuoride ions can be added to the bath to maintain and to regulatethe catalyst acid radical content of the bath. Silicofiuoride ions canbe added in the form of fiuosilicic acid. Also, they can be added assilicofluoride salt or salts with a cation that does not affectadversely the bath characteristics such as potassium, sodium, magnesium,and chromium. The silicofluoride ion is usually present in an amountequal to about 1% to 2% of the chromic acid concentration.

The examples below are illustrative of typical bath formulations.

Example I Ounces per gallon Chromic acid (CrO 27 to 67 Strontium sulfate0.8-1 to 2.01 Potassium silicofiuoride 2.16 to 5.36

Example II Chromic acid (CrO 40 Sulfuric acid 0.24 Fluosilicic acid;0.40

The stable additive compositions of this invention are soluble inconventional aqueous acidic hexavalent chromium baths and will and mist.Furthermore, the additive compositions are stable'to the extremelypowerful oxidizing conditions that exist at the insoluble anodes duringthe electro-deposition of chromium from such baths.

The stable additive composition of this inventioncomprises specificnon-ionic wetting agents alone or in admixture with certain alkylaromatic sulfonates to be detailed more fully hereinafter. The non-ionicwetting agents or surfactants are selected from the group consisting of(1) polymers of ethylene oxide having an average molecular weight offrom about 1,300 to 1,800, (2) a cogeneric mixture of conjugatedpolyoxypropylenepolyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of a reactive hydrogen atom to therebyconstitute a polyoxypropylene polymer, the oxyethylene groups areattached to the polyoxypropylene polymer in polyoxyethylene chains, theaverage molecular weight 'of the polyoxypropylene polymer in the mixtureis within the range of from about 1,500 to 1,800, as determined byhydroxyl number, and the oxyethylene groups present constitute fromabout 80% to by weight of the mixture, and (3) mixtures of (1) and (2).

Nonionic Wetting agent (2) above can be represented by the structuralformula prevent or minimize effectively the 3 wherein Y represents aninteger sufi'icient to provide a molecular weight of polyoxypropylene offrom 1500 to 1800, and X and Z are in integers the total of which issufiicient to provide oxyethylene groups in an amount equal to fromabout 80% to 95% by Weight of the total weight of the molecule.

Compounds of the types above described under (2) are availablecommercially under the proprietary designation Pluronic.

It has been determined also, according to the present invention, thatsubstantial reduction of the undesired chromic acid spray can beaccomplished by adding to the bath an admixture of from to 90 parts byweight of the above enumerated nonionic wetting agents (1), (2), and (3)and from 90 to 10 parts by weight of an alkyl aromatic sulfonic acidcompound of the benzene series containing at least 7 carbon atoms in analkyl group.

While the specific nonionic wetting agents (1), (2), and (3) enumeratedabove are effective in reducing substantially the chromic acid spray, itis preferred to employ the admixture as set forth hereinbelow as it iseven more eifective. The preferred admixture will comprise from 40 to 60parts by Weight of nonionic wet-ting agent (1), (2), or (3) and fiom 60to 40 parts by weight of alkyl aromatic sulfonic acid compound of thebenzene series containing at least 7 carbon atoms in an alkyl group.

Alkyl aromatic sulfonic acid compounds of the benzene series containingat least 7 carbon atoms in an alkyl group can be represented by theformula in which X represents hydrogen; a hydroxyl group; a lower alkylgroup such as methyl, ethyl, propyl, isopropyl, and n-butyl; analkoxygroup such as methoxy, ethoxy, benzyloxy and the like; an aryloxy groupsuch as phenoxy and methylphenoxy; or a carboxyl group. R represents analkyl hydrocarbon radical (saturated or unsaturated) containing 7 ormore (preferably 10 to 19) carbon atoms, and M represents hydrogen or ametal, or an ammonium or an organic ammonium radical. For conveniencethis'class of compounds will be referred to hereinafter as alkylaromatic sulfonates of the benzene series.

Reference is made to US. Patent 2,195,409 for a more detaileddescription of alkyl aromatic sulfonates of the benzene series, specificexamples thereof, and methods of preparing the same.

The following specific example is given by way of illustration. Allparts are by weight unless otherwise designated.

Example III One hundred parts of commercial lauryl alcohol (obtained byhydrogenation of fatty acids from cocoanut oil), 100 parts of phenol,and 100 parts of anhydrous zinc chloride are mixed and refluxed at 190C. to 200 C. with agitation for about 16 hours. The condensation productis washed with water until substantially free of water-soluble products,and the resulting oil is fractionally distilled in vacuo. The fractionof the distillate collected as a faint yellow to water-white oil between210 C. to 230 C. at 13 mm. mercury pressure consists mainly of laurylphenols of which the probable formula of the main constituent is areadded to 270 parts of the resulting oil which is held at a temperaturebelow 10 C., then sulfonation is continued at room temperature for 2hours. The sulfonation mixture is drowned in four times its weight of amixture of ice and water and a solution of sodium hydroxide is addedwhile keeping the temperature below 35 C. until the product is neutral(pI-l=7.0). The neutralized solution is evaporated to dryness to providean alkyl aromatic sulfonate of the benzene series suitable for use inthis invention.

The amount of stable additive composition of this invention that isadded to the chromium electroplating bath will be sufficient to providea bath surface tension of at least 55 dynes per cm. at 25 C. It has beendetermined that the stable additive composition of this invention,Whether it comprise the above defined nonionic wet-ting agents alone orthe nonionic wetting agents in admixture with the alkyl aromaticsulfonates of the benzene series, can be added in amount of from about.015 to .40 ounce per gallon of electrolyte. It is within the skill ofthose versed in the art to determine the amount of additivecomposition'required to provide a bath surface tension of at least 55dynes per cm. at 25 C., or at least an amount sufficient to retardsubstantially the liberation of chromic acid fumes or spray from thebath.

The non-ionic wetting agents alone provide for substantial reduction ofthe surface tension of the chromium electroplating bath and issatisfactory for most baths. However, for baths of higher chromic acidconcentration it is preferred to employ the admixture of non-ionicwetting agent acid alkyl aromatic sulfonates as above defined as thesurface tension of the bath is more elfectively controlled therebyeliminating substantially any undesired chromic acid spray.

The examples that follow are illustrative of this invention.

Example IV To a chromic acid bath containing 54 ounces of CrO; pergallon of aqueous solution and a ratio of HSO :CrO within the range of1:100 there is added .20 ounce per gallon of a non-ionic wetting agentconsisting of a cogeneric mixture of conjugatedpoloxypropylene-polyoxyethylene compounds containing in their structurecxyproylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatorns, the compounds being characterized in that all of theoxypropylene groups are present in polyoxypropylene chains that areattached to the organic radical at the site of the reactive hydrogenatom to thereby constitute a polyoxypropylene polymer, the oxyethylenegroups are attached to the polyoxypropylene polymer in polyoxyethylenechains, the average molecular weight of the polyoxypropylene polymer inthe mixture is about 1500 to 1800 as determined by hydroxyl number, andthe oxyethylene groups present constitute about by weight of themixture. During operation of this bath, substantially no chromic acidspray or mist is noted.

Example V Achromium plating bath is prepared as described in Example IVabove except that 40 ounces of CrO are employed per gallon of solutionand .20 ounce per gallon of a polymer of ethylene oxide having amolecular weight of about 1500. Excellent results are obtained inplating various types of objects in this bath and there is substantiallyno chromic acid spray or mist noted.

To the chromium plating bath of Example II there is added about .30ounce per gallon of a stable additive composition consisting of, byweight, 5 0 parts of the nonionic Wetting agent used in Example IV and50 parts of the alkyl aromatic sulfonate of the benzene series ofExample III. Good plating results are obtained and no objectionablechromic acid spray is noted.

The operating conditions for the bath of this invention are the same asthose employed for the baths without the addition of the stable additivecomposition of this invention. Thus, operating temperatures of fromabout C. to 160 C. can be employed, and current densities of from about100 to 500 amperes per square foot are satisfactory.

A significant reduction in the spray and mist formed duringelectrodeposition of chromium from aqueous acidic hexavalent chromiumbaths is apparent when the additive composition of this invention isemployed. Further the additive compositions of this invention are verystable. That is they do not decompose in the chromium bath and losetheir effectiveness.

It is to be understood that the above description of this invention isillustrative only and not in limitation thereof. F

We claim as our invention:

1. A chromic acid plating bath for the electrodeposition of chromiumcomprising an aqueous acidic hexavalent chromium solution containing anon-ionic wetting agent selected from the group consisting of (1)polymers of ethylene oxide having an average molecular weight of from1300 to 1800, (2) a cogeneric mixture of conjugatedpolyoxypropylene-polyoxyethylene compounds containa ing in theirstructure oxypropylene groups, oxyethylene groups and an organic radicalderived from an organic compound containing a plurality of reactivehydrogen atoms, the compounds being characterized in that all of theoxypropylene groups are present in polyoxypropylene chains that areattached to the organic radical at the site of a reactive hydrogen atomto thereby constitute a polyoxypropylene polymer, the oxyethylene groupsare attached to the polyoxypropylene polymer in polyoxye'thylene chains,the average molecular weight of the polyoxypropylene polymer in themixture being from about 1500 to 1800 as determined by hydroxyl number,and the oxyethylene groups present constitute from about 80% to 95% byWeight of the mixture, and (3) mixtures of (l) and (2), said non-ionicWetting agent being present in an amount sufiicient to retardsubstantially the liberation of chromic acid fumes from said bath.

2. A chromic acid plating bath for the electrodeposition of chromiumcomprising an aqueous acidic hexavalent chromium solution containing astable additive composition comprising (A) from to 90 parts by Weight ofa non-ionic Wetting agent selected from the group consisting of (l)polymers of ethylene oxide having an average molecular weight of from1300 to 1800, (2) a cogeneric mixture of conjugatedpolyoxypropylene-polyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of the reactive hydrogen atom to therebyconstitute a polyoxy-propylene polymer, the oxyethylene groups areattached to the polyox-ypropylene polymer in polyoxyethylene chains, theaverage molecular weight of the polyoxypropylene polymer in the mixturebeing from about 1500 to 1800 as determined by hydroxyl number,

and the oxyethylene groups present constitute from about 80% to 95% byWeight of the mixture and (3) mixtures of (1) and (2), and (B) from 90parts to 10 parts by Weight of an alkyl aromatic sulfonic acid comwundof the benzene series containing at least 7 carbon atoms in an 1 alkylgroup, said stable additive composition being present in an amountsufiicient to retard substantially the liberation of chromic acid fumesfrom said bath.

3. A chromic acid plating bath for the electrodeposition of chromiumcomprising an aqueous acidic hexavalent chromium solution containing astable additive composition comprising (A) from 40 to 60' parts byWeight of a non-ionic lwetting agent selected from the group consistingof (1) polymers of ethylene oxide having an average molecular Weight offrom 1300 to 1800', (2) a cogeneric mixture of conjugatedpolyoxyproplyene-polyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of theoxy-propylene groups are present in polyoxypropylene chains that areattached to the organic radical at the site of the reactive hydrogenatom to thereby constitute a polyoxypropylene polymer, the oxyethylenegroups are attached to the polyoxypropylene polymer in polyoxyethylenechains, the average molecular Weight of the polyoxypropylene polymer inthe mixture being from about 1500 to 1800 as determined by hydroxylnumber, and the oxyethylene groups present constitute from about to 95by weight of the mixture, and (3) mixtures of (l) and (2), and (B) from60 parts to 40 parts by weight of an alkyl aromatic sulfonic acidcompound of the benzene series containing at least 7 carbon atoms in analkyl group, said stable additive composition being present in an amountsuflicient to retard substantially the liberation of chromic acid fumesfrom said bath.

4. The method of chromium plating which comprises electrodepositingchromium from a chromic acid plating bath comprising a non-ionic Wettingagent selected from the group consisting of (1) polymers of ethyleneoxide having an average molecular weight of from 1300 to 1800, (2) acogeneric mixture of conjugated polyoxypropylene-polyoxyethylenecompounds containing in their structure oxypropylene groups, oxyethylenegroups and an organic radical derived from an organic compoundcontaininga plurality of reactive hydrogen atoms, the compounds beingcharacterized in that all of the oxypropylene groups are present inpolyoxypropylene chains that are attached to the organic radical at thesite of the reactive hydrogen atom to thereby constitute apolyoxypropylene polymer, the oxyethylene groups are attached to thepolyoxypropylene polymer in polyoxyethylene chains, the averagemolecular Weight of the polyoxypropylene polymers in the mixture is fromabout 1500 to 1800 as determined by hydroxyl number, and the oxyethylenegroups present constitute from about 80% to 95% by Weight of themixture, and (3) mixtures of (1) and (2), said nonionic wetting agentbeing present in an amount sufiicient to retard substantially theliberation of chromic acid fumes from said bath.

5. The method of chromium plating which comprises electrodepositingchromium from a chromic acid plating bath comprising a stable additivecomposition comprising (A) from 10 to parts by weight of a non-ionicwetting agent selected from the group consisting of (1) polymers ofethylene oxide having an average molecular Weight of from about 1300 to1800, (2) a cogeneric mixture of conjugatedpolyoxypropylene-polyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of a reactive hydrogen atom to therebyconstitute a polyoxypropylene polymer, the oxyethylene groups areattached to the polyoxypropylene polymer in polyoxyethylene chains, theaverage molecular Weight of the polyoxypropylene polymer in the mixturebeing Within the range of from about 1500 to 1800 as deter-, mined byhydroxyl number, and the oxyethylene groups present constitute fromabout 80% to by Weight of the mixture, and (3) mixtures of (1) and (2),and (B) from 90 parts to 10 parts by :weight of an alkyl aro maticsulfonic acid compound of the benzene series containing at least 7carbon atoms in an 'alkyl group, said 'stable additive composition beingpresent in an amount suflicient to retard substantially the liberationof chromic acid fumes from said bath.

6. The method of chromium plating Which comprises electrodepositingchromium from a chromic acid plating bath comprising a stable additivecomposition comprising (A) from 40 to 60 parts by weight of a non-ionicWetting agent selected from the group consisting or" (1) polymers ofethylene oxide having an average molecular weight of from about 1300 to1800, (2) a cogeneric mixture of conjugatedpolyoxypropylene-polyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of a reactive hydrogen atom to therebyconstitute a polyoxypropylene polymer, the oxyethylene groups areattached to the polyoxypropylene polymer in polyoxyethylene chains, theaverage molecular weight of the polyoxypropylene polymer in the mixturebeing Within the range of from about 1500 to 1800 as determined byhydroxyl number, and the oxyethylene groups present constitute fromabout 80% to 95% by weight of the mixture, and (3) mixtures of (1) and(2), and (B) from 60 parts to 40 parts by weight of an alkyl aromaticsulfonic acid compound of the benzene series containing at least 7carbon atoms in an alkyl group, said stable additive composition beingpresent in an amount suificient to retard substantially the liberationof chrorric acid fumes from said bath.

7. A chromic acid plating bath for the electro-deposition of chromiumcomprising an aqueous solution of from about 33 ounces to 54 ounces pergallon of CrO an amount of H 80, suflicient to provide a weight ratio ofH SO :CrO of 1:250 to 1:60 and a quantity of non ionic Wetting agentselected from the group consisting of (1) polymers of ethylene oxidehaving an average molecular weight of from about 1300 to 1800, (2) acogeneric mixture of conjugated polyoxypropylene-polyoxyethylenecompound containing in their structure oxypropylene groups,oxyethylenegroups and an organic radical derived from an organiccompound containing a plurality of reactive hydrogen atoms, the compoundbeing characterized in that all of the oxypropylene groups are presentin polyoxypropylene chains that are attached to the organic radical atthe site of a reactive hydrogen atom to thereby constitute apolyoxypropylene polymer, the oxyethylene groups are attached to thepolyoxypropylene polymer in polyoxyethylene chains, the averagemolecular Weight of the polyoxypropylene polymers in the mixture is fromabout :1500 to 1800 as determined by hydroxyl number, and theoxyethylene groups present constitute from about 80% to 95% by weight ofthe mixture, and (3) mixtures of (1) and (2) said non-ionic Wettingagent being present in an amount sufiicient to retard substantially theliberation of chromic acid fumes from said bath.

8. A chromic acid plating bath for the electrodeposition of chromiumcomprising an aqueous solution of from about 33 ounces to 54 ounces pergallon of CrO an amount of H 50 sufiicient to provide a ratio of H SO:CrO of 1:250 to 1:60 and a quantity of a stable additive compositioncomprising (A) from 10 to 90 parts by weight of non-ionic wetting agentselected from the group consisting of (l) polymers of ethylene oxidehaving an average molecular Weight of from about 1300 to 1 800, (2) acogeneric mixture of conjugated polyoxypropylene-polyoxyethylenecompounds containing in their structure oxypropylene groups, oxyethylenegroups and an organic radical derived from an organic compoundcontaining a plurality of reactive hydrogen atoms, the compound beingcharacterized in that all of the oxypropylene groups are present inpolyoxypropylene chains that are attached to the organic radical at thesite of the reactive hydrogen atom to thereby constitute apolyoxypropylene polymer, the oxyethylene groups are atattached to thepolyoxypropylene polymer in polyoxyethylene chains, the averagemolecular weight of the polyoxypropylene polymers in the mixture beingfrom about 1500 to 1800 as determined by hydroxyl number, and theoxyethylene groups present constitute from about 80% to 95% by weight ofthe mixture, and (3) mixtures of (l) and (2), and (B) from 90 parts to10 parts by Weight of an alkyl aromatic sulfonic acid compound of thebenzene series containing at least 7 carbon atoms in an alkyl group saidstable additive composition being present in an amount suflicient toretard substantially the liberation of chromic acid fumes and spray fromsaid bath.

9. A chromic acid plating bath for the electrodeposition of chromiumcomprising an aqueous solution of from about 33 ounces to 54 ounces pergallon of C10 an amount of H 80 suificient to provide a ratio of H SO:CrO of 1:250 to 1:60 and a quantity of a stable additive compositioncomprising (A) from 40 to 60 parts by weight of a non-ionic Wettingagent selected from the group consisting of (1) polymers of ethyleneoxide having an average molecular Weight of from about 1300 to 1800, (2)a cogeneric mixture of conjugated polyoxypropylene-polyoxyethylenecompounds containing in their structure oxypropylene groups, oxyethylenegroups and an organic radical derived from an organic compoundcontaining a plurality of reactive hydrogen atoms, the compound beingcharacterized in that all of the oxypropylene groups are present inpolyoxypropylene chains that are, attached to the organic radical at thesite of the reactive hydrogen atom to thereby constitute apolyoxypropylene polymer, the oxyethylene groups are attached to thepolyoxypropylene polymer in polyoxyethylene chains, the averagemolecular weight of the polyoxypropylene polymers in the mixture beingfrom about 1500 to 1800 as determined by hydroxyl number, and theoxyethylene groups present constitute from about 80% to 95% by Weight ofthe mixture, and (3) mixtures of (1) and (2), and (B) from 60 parts to40 parts by weight of an alkyl aromatic sulfonic acid compound of thebenzene series containing at least 7 carbon atoms in an alkyl group saidstable additive composition present in an amount suflicient to retardsubstantially the liberation of chromic acid fumes and spray from saidbath.

10. A stable additive composition for addition to chromic acid platingbaths whereby the liberation of chromic acid fumes from said bathsduring use is retarded substantially comprising (A) from 10 to 90 partsby weight of a non-ionic Wetting agent selected from the groupconsisting of (1) polymers of ethylene oxide having an average molecularweight of from 1300 to 1800, (12) a cogeneric mixture of conjugatedpolyoxypropylene-polyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of the reactive hydrogen atom to therebyconstitute a polyoxypropylene polymer, the oxyethylene groups areattached to the polyoxypropylene polymer in polyoxyethylene chains, theaverage molecular weight of the polyoxypropylene polymer in the mixturebeing from about 1500 to 1800 as determined by hydroxyl number, and theoxyethylene groups present constitute from about 80% to 95% by Weight ofthemixture, and (3) mixtures of (1) and (2), and (B) from parts to 10parts by weight of an alkyl aromatic sulfonic acid compound of thebenzene series containing at least 7 carbon atoms in an alkyl group,said stable additive composition being present in an amount sufficientto retard sub- 1itantially the liberation of chromic acid fumes fromsaid ath.

11. A stable additive composition for addition to chromic acid platingbaths whereby the liberation of chromic acid fumes from said bathsduring use is retarded substantially comprising (A) from 40 to 60 partsby weight of a non-ionic Wetting agent selected from the groupconsisting of (1) polymers of ethylene oxide having an average molecularweight of from 1300 to 1800, (2) a cogeneric mixture of conjugatedpolyoxypropylenepolyoxyethylene compounds containing in their structureoxypropylene groups, oxyethylene groups and an organic radical derivedfrom an organic compound containing a plurality of reactive hydrogenatoms, the compounds being characterized in that all of the oxypropylenegroups are present in polyoxypropylene chains that are attached to theorganic radical at the site of the reactive hydrogen atom to therebyconstitute a polyoxypropylene polymer, the oxyethylene groups areattached to the polyoxypropylene polymer in polyoxyethylene chains, theaverage molecular Weight of the polyoxypropylene polymer in the mixturebeing from about 1500 to 1800 as determined by hydroxyl number, and theoxyethylene groups present References Cited in the file of this patentUNITED STATES PATENTS 2,115,192 Bruson Apr. 26, 1938 2,195,409 FlettApr. 2, 1940 2,213,477 Steindorfi et al Sept. 3, 1940 2,655,471 ChesterOct. 13, 1953 OTHER REFERENCES Pluronics, Wyandotte Chemical Corp., 9pages, received in Patent Oflice J an. 7, 1957.

1. A CHROMAIC ACID PLATING BATH FOR THE ELECTRODEPOSITION OF CHROMIUMCOMPRISING AN AQUEOUS ACIDIC HEXAVALENT CHROMIUM SOLUTION CONTAINING ANON-IONIC WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF (1)POLYMERS OF ETHYLENE OXIDE HAVING AN AVERAGE MOLECULAR WEIGHT OF FROM1300 TO 1800, (2) A COGENERIC MIXTURE OF CONJUGATEDPOLYOXYPROPYLENE-PROLYOXYETHYLENE COMPOUNDS CONTAINING IN THEIRSTRUCTURE OXYPROPYLENE GROUPS, OXYETHYLENE GROUPS AND AN ORGANIC RADICALDERIVED FROM AN ORGANIC COMPOUND CONTAINING A PLURALITY OF REACTIVEHYDROGEN ATOMS, THE COMPOUNDS BEING CHARATERIZED IN THAT ALL OF THEOXYPROPYLENE GROUPS ARE PRESENT IN PLOYOXYPROPYLENE CHAINS THAT AREATTACHED TO THE ORGANIC RADICAL AT THE SITE OF A REACTIVE HYDROGEN ATOMTO THEREBY CONSTITUTE A POLYOXYPROPYLENE POLYMER, THE OXYETHYLENE GROUPSARE ATTACHED TO THE POLYOXYPROPYLENE POLYMER IN POLYOXYETHYLENE CHAINSTHE AVERAGE MOLECULAR WEIGHT OF THE POLYOXYPROPYLENE POLYMER IN THEMIXTURE BEING FROM ABOUT 1500 TO 1800 AS DETERMINED BY HYDROXYL NUMBER,AND THE OXYETHYLENE GROUPS PRESENT CONSTITUTE FROM ABOUT 80% 95% BYWEIGHT OF THE MIXTURE, AND (3) MIXTURES OF (1) AND (2) SAID NON-IONICWETTING AGENT BEING PRESENT IN AN AMOUNT SUFFICIENT TO RETARDSUBSTANTIALLY THE LIBERATION OF CHROMIC ACID FUMES FROM SAID BATH.